Readme: visually separate phpunit version specific paragraphs

Author: staabm

README.md

@@ -72,6 +72,8 @@ adjust your `phpunit.xml` configuration file and configure the
  </phpunit>
 ```
 
+---
+
 To bootstrap the extension as a `composer` package when using
 
 - `phpunit/phpunit:^7.5.0`
@@ -101,6 +103,8 @@ adjust your `phpunit.xml` configuration file and configure the
  </phpunit>
 ```
 
+---
+
 To bootstrap the extension as a `composer` package when using
 
 - `phpunit/phpunit:^10.0.0`
@@ -162,6 +166,8 @@ adjust your `phpunit.xml` configuration file and configure the
  </phpunit>
 ```
 
+---
+
 To bootstrap the extension as a PHAR when using
 
 - `phpunit/phpunit:^10.0.0`
@@ -242,6 +248,8 @@ The following example configures the maximum count of slow tests to three, and t
  </phpunit>
 ```
 
+---
+
 To configure the extension when using
 
 - `phpunit/phpunit:^7.5.0`
@@ -285,6 +293,8 @@ The following example configures the maximum count of slow tests to three, and t
  </phpunit>
 ```
 
+---
+
 To configure the extension when using
 
 - `phpunit/phpunit:^10.0.0`